Method for depositing tungsten-containing layers by vapor deposition techniques

ABSTRACT

In one embodiment, a method for forming a tungsten-containing material on a substrate is provided which includes forming a tungsten-containing layer by sequentially exposing a substrate to a processing gas and a tungsten-containing gas during an atomic layer deposition process, wherein the processing gas comprises a boron-containing gas and a nitrogen-containing gas, and forming a tungsten bulk layer over the tungsten-containing layer by exposing the substrate to a deposition gas comprising the tungsten-containing gas and a reactive precursor gas during a chemical vapor deposition process. In one example, the tungsten-containing layer and the tungsten bulk layer are deposited within the same processing chamber.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 11/461,909(APPM/004714.C5), filed Aug. 2, 2006, which is a continuation of U.S.Ser. No. 09/678,266 (APPM/004714.P1), filed Oct. 3, 2000, and issued asU.S. Pat. No. 7,101,795, which is a continuation-in-part of U.S. Ser.No. 09/605,593 (APPM/004714), filed Jun. 28, 2000, and issued as U.S.Pat. No. 6,551,929, which are herein incorporated by reference in theirentirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the processing of semiconductor substrates.More particularly, this invention relates to improvements in the processof depositing refractory metal layers on semiconductor substrates.

2. Description of the Related Art

The semiconductor processing industry continues to strive for largerproduction yields while increasing the uniformity of layers deposited onsubstrates having larger surface areas. These same factors incombination with new materials also provide higher integration ofcircuits per unit area of the substrate. As circuit integrationincreases, the need for greater uniformity and process control regardinglayer thickness rises. As a result, various technologies have beendeveloped to deposit layers on substrates in a cost-effective manner,while maintaining control over the characteristics of the layer.Chemical Vapor Deposition (CVD) is one of the most common depositionprocesses employed for depositing layers on a substrate. CVD is aflux-dependent deposition technique that requires precise control of thesubstrate temperature and precursors introduced into the processingchamber in order to produce a desired layer of uniform thickness. Theserequirements become more critical as substrate size increases, creatinga need for more complexity in chamber design and gas flow technique tomaintain adequate uniformity.

A variant of CVD that demonstrates superior step coverage, compared toCVD, and is Atomic Layer Deposition (ALD). ALD is based upon AtomicLayer Epitaxy (ALE) that was employed originally to fabricateelectroluminescent displays. ALD employs chemisorption to deposit asaturated monolayer of reactive precursor molecules on a substratesurface. This is achieved by alternatingly pulsing an appropriatereactive precursor into a deposition chamber. Each injection of areactive precursor is separated by an inert gas purge to provide a newatomic layer additive to previously deposited layers to form a uniformlayer on the substrate. The cycle is repeated to form the layer to adesired thickness. A drawback with ALD techniques is that the depositionrate is much lower than typical CVD techniques by at least one order ofmagnitude.

Formation of film layers at a high deposition rate while providingadequate step coverage are conflicting characteristics oftennecessitating sacrificing one to obtain the other. This conflict is trueparticularly when refractory metal layers are deposited to cover gaps orvias during formation of contacts that interconnect adjacent metalliclayers separated by dielectric layers. Historically, CVD techniques havebeen employed to deposit conductive material such as refractory metalsin order to inexpensively and quickly form contacts. Due to theincreasing integration of semiconductor circuitry, tungsten has beenused based upon superior step coverage. As a result, deposition oftungsten employing CVD techniques enjoys wide application insemiconductor processing due to the high throughput of the process.

Depositing tungsten by traditional CVD methods, however, is attendantwith several disadvantages. For example, blanket deposition of atungsten layer on a semiconductor wafer is time-consuming attemperatures below 400° C. The deposition rate of tungsten may beimproved by increasing the deposition temperature to, e.g., about 500°C. to about 550° C.; however, temperatures in this higher range maycompromise the structural and operational integrity of the underlyingportions of the integrated circuit being formed. Use of tungsten hasalso frustrated photolithography steps during the manufacturing processas it results in a relatively rough surface having a reflectivity of 20%or less than that of a silicon substrate. Finally, tungsten has provendifficult to deposit uniformly. Variance in film thickness of greaterthan 1% has been shown with tungsten, thereby frustrating control of theresistivity of the layer. Several prior attempts to overcome theaforementioned drawbacks have been attempted.

For example, in U.S. Pat. No. 5,028,565 to Chang et al., which isassigned to the assignee of the present invention, a method is disclosedto improve, inter alia, uniformity of tungsten layers by varying thedeposition chemistry. The method includes, in pertinent part, formationof a nucleation layer over an intermediate barrier, layer beforedepositing the tungsten layer via bulk deposition. The nucleation layeris formed from a gaseous mixture of tungsten hexafluoride, hydrogen,silane, and argon. The nucleation layer is described as providing alayer of growth sites to promote uniform deposition of a tungsten layerthereon. The benefits provided by the nucleation layer are described asbeing dependent upon the barrier layer present. For example, were thebarrier layer formed from titanium nitride the tungsten layer'sthickness uniformity is improved as much as 15%. Were the barrier layerformed from sputtered tungsten or sputtered titanium tungsten, thebenefits provided by the nucleation layer are not as pronounced.

U.S. Pat. No. 5,879,459 to Gadgil et al. discloses an apparatus thattakes advantage of ALD. To that end, the apparatus, a low profile,compact atomic layer deposition reactor (LP-CAR), has a body with asubstrate processing region adapted to serve a single substrate or aplanar array of substrates, as well as a valve, and a port for substrateloading and unloading. In some embodiments multiple reactors are stackedvertically and share a common robotic handler interface with a CVDsystem. In this manner, the robotic handler may manipulate substratesassociated with both the CVD system and the LP-CAR. The compact reactoris distinguished by having individual injectors, each of which comprisesa charge tube formed between a charge valve and an injection valve. Thecharge valve connects the charge tube to a pressure regulated supply,and the injection valve opens the charge tube into the compact reactor.Rapidly cycling the valves injects fixed mass-charges of gas or vaporinto the compact reactor.

What is needed, however, is a technique to deposit conductive layershaving a deposition rate comparable to CVD techniques while providingthe step coverage associated with ALD techniques.

SUMMARY OF THE INVENTION

A method and system to form a refractory metal layer on a substratefeatures nucleating a substrate using sequential deposition techniquesin which the substrate is serially exposed to first and second reactivegases followed by forming a layer, employing vapor deposition, tosubject the nucleation layer to a bulk deposition of a compoundcontained in one of the first and second reactive gases. To that end,the system includes a processing chamber that has a holder disposedtherein to support the substrate. A gas delivery system and a pressurecontrol system is in fluid communication with the processing chamber. Atemperature control system is in thermal communication therewith. Acontroller is in electrical communication with gas delivery systems,temperature control systems, pressure control systems. A memory is indata communication with the controller. The memory comprises acomputer-readable medium having a computer-readable program embodiedtherein. The computer readable program includes instructions forcontrolling the operation of the processing chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a semiconductor processing system inaccordance with the present invention;

FIG. 2 is a detailed view of the processing chambers shown in FIG. 1;

FIG. 3 is a schematic view showing deposition of a first molecule onto asubstrate during ALD;

FIG. 4 is a schematic view showing deposition of second molecule onto asubstrate during ALD to form a refractory metal layer;

FIG. 5 is a graphical representation showing the concentration of gases,introduced into the processing chamber shown in FIG. 2, and the time inwhich the gases are present in the processing chamber, in accordancewith the present invention;

FIG. 6 is a graphical representation showing the relationship betweenthe number of ALD cycles and the thickness of a layer formed on asubstrate employing ALD, in accordance with the present invention;

FIG. 7 is a graphical representation showing the relationship betweenthe number of ALD cycles and the resistivity of a layer formed on asubstrate employing ALD, in accordance with the present invention;

FIG. 8 is a graphical representation showing the relationship betweenthe deposition rate of a layer formed on a substrate employing ALD andthe temperature of the substrate;

FIG. 9 is a graphical representation showing the relationship betweenthe resistivity of a layer formed on a substrate employing ALD and thetemperature of the substrate, in accordance with the present invention;

FIG. 10 is a cross-sectional view of a patterned substrate having anucleation layer formed thereon employing ALD, in accordance with thepresent invention;

FIG. 11 is a partial cross-sectional view of the substrate, shown inFIG. 10, with a refractory metal layer formed atop of the nucleationlayer employing CVD, in accordance with the present invention; and

FIG. 12 is a graphical representation showing the concentration of gasesshown in FIG. 3, in accordance with a first alternate embodiment of thepresent invention.

DETAILED DESCRIPTION

Referring to FIG. 1, an exemplary wafer processing system includes oneor more processing chambers 12 and 14 disposed in a common work area 16surrounded by a wall 18. The processing chambers 12 and 14 are in datacommunication with a controller 22 that is connected to one or moremonitors, shown as 24 and 26. The monitors typically display commoninformation concerning the process associated with the processingchambers 12 and 14. One of the monitors 26 is mounted to the wall 18,with the remaining monitor 24 being disposed in the work area 16.Operational control of the processing chambers 12 and 14 may be achievedby the use of a light pen, associated with one of the monitors 24 and26, to communicate with the controller 22. For example, light pen 28 isassociated with monitor 24 and facilitates communication with thecontroller 22 through monitor 24. Light pen 29 facilitates communicationwith the controller 22 through monitor 26.

Referring both the to FIGS. 1 and 2, each of the processing chambers 12and 14 includes a housing 30 having a base wall 32, a cover 34, disposedopposite to the base wall 32, and a sidewall 36, extending therebetween.The housing 30 defines a chamber 37, and a pedestal 38 is disposedwithin the processing chamber 37 to support a substrate 42, such as asemiconductor wafer. The pedestal 38 may be mounted to move between thecover 34 and the base wall 32, using a displacement mechanism (notshown), but the position thereof is typically fixed. Supplies ofprocessing gases 39 a, 39 b, and 39 c are in fluid communication withthe processing chamber 37 via a showerhead 40. Regulation of the flow ofgases from the supplies 39 a, 39 b, and 39 c is effectuated via flowvalves 41.

Depending on the specific process, the substrate 42 may be heated to adesired temperature prior to layer deposition via a heater embeddedwithin the pedestal 38. For example, the pedestal 38 may be resistivelyheated by applying an electric current from an AC power supply 43 to theheater element 44. The substrate 42 is, in turn, heated by the pedestal38, and can be maintained within a desired process temperature range of,for example, about 20° C. to about 750° C. A temperature sensor 46, suchas a thermocouple, is also embedded in the wafer support pedestal 38 tomonitor the temperature of the pedestal 38 in a conventional manner. Forexample, the measured temperature may be used in a feedback loop tocontrol the electrical current applied to the heater element 44 by thepower supply 43 such that the substrate temperature can be maintained orcontrolled at a desired temperature that is suitable for the particularprocess application. Optionally, the pedestal 38 may be heated usingradiant heat (not shown). A vacuum pump 48 is used to evacuate theprocessing chamber 37 and to help maintain the proper gas flows andpressure inside the processing chamber 37.

Referring to FIGS. 1 and 3, one or both of the processing chambers 12and 14, discussed above may operate to deposit refractory metal layerson the substrate employing sequential deposition techniques. One exampleof sequential deposition techniques in accordance with the presentinvention includes atomic layer deposition (ALD). Depending on thespecific stage of processing, the refractory metal layer may bedeposited on the material from which the substrate 42 is fabricated,e.g., SiO₂. The refractory metal layer may also be deposited on a layerpreviously formed on the substrate 42, e.g., titanium, titanium nitride,and the like.

During the sequential deposition technique in accordance with thepresent invention, a batch of a first processing gas, in this caseAa_(x), results in a layer of A being deposited on the substrate 42having a surface of ligand a exposed to the processing chamber 37.Thereafter, a purge gas enters the processing chamber 37 to purge thegas Aa_(x). After purging gas Aa_(x) from the processing chamber 37, asecond batch of processing gas, Bb_(y), is introduced into theprocessing chamber 37. The a ligand present on the substrate surfacereacts with the b ligand and B atom on the releasing molecules ab andBa, that move away from the substrate 42 and are subsequently pumpedfrom the processing chamber 37. In this manner, a surface comprising alayer of A compound remains upon the substrate 42 and exposed to theprocessing chamber 37, shown in FIG. 4. The composition of the layer ofA may be a monolayer of atoms typically formed employing ALD techniques.Alternatively, the layer of A may include a layer of multiple atoms. Insuch as case, the first processing gases may include a mixture ofprocess gases each of which has atoms that would adhere to the substrate42. The process proceeds cycle after cycle, until the desired thicknessis achieved.

Referring to both FIGS. 2 and 5, although any type of processing gas maybe employed, in the present example, the processing gas Aa_(x) includesWF₆ and the processing gas Bb_(y) is B₂H₆. Two purge gases are employed:Ar and N₂. Each of the processing gases was flowed into the processingchamber 37 with a carrier gas, which in this example were one of thepurge gases: WF₆ is introduced with Ar and B₂H₆ is introduced with N₂.It should be understood, however, that the purge gas may differ from thecarrier gas, discussed more fully below. One cycle of the ALD techniquein accordance with the present invention includes flowing the purge gas,N₂, into the processing chamber 37 during time t₁, which isapproximately 0.01 seconds to 15 seconds before B₂H₆ is flowed into theprocessing chamber 37. During time t₂, the processing gas B₂H₆ is flowedinto the processing chamber 37 for a time in the range of 0.01 secondsto 15 seconds, along with a carrier gas, which in this example is N₂.After 0.01 seconds to 15 seconds have lapsed, the flow of B₂H₆terminates and the flow of N₂ continues during time t₃ for an additionaltime in the range of 0.01 seconds to 15 seconds, purging the processingchamber of B₂H₆. During time t₄, the processing chamber 37 is pumped soas to remove most, if not all, gases. After pumping of the processchamber 37, the carrier gas Ar is introduced for a time in the range of0.01 seconds to 15 seconds during time t₅, after which time the processgas WF₆ is introduced into the processing chamber 37, along with thecarrier gas Ar during time t₆. The time t₆ lasts between 0.01 seconds to15 seconds. The flow of the processing gas WF₆ into the processingchamber 37 is terminated approximately 0.01 seconds to 15 seconds afterit commenced. After the flow of WF₆ into the processing chamber 37terminates, the flow of Ar continues for an additional time in the rangeof 0.01 seconds to 15 seconds, during time t₇. Thereafter, theprocessing chamber 37 is pumped so as to remove most, if not all, gasestherein, during time t₈. As before, the pumping process lastsapproximately thirty seconds, thereby concluding one cycle of thesequential deposition technique in accordance with the presentinvention.

The benefits of employing the sequential deposition technique aremanifold, including flux-independence of layer formation that providesuniformity of deposition independent of the size of a substrate. Forexample, the measured difference of the layer uniformity and thicknessmeasured between a 200 mm substrate and a 32 mm substrate deposited inthe same chamber is negligible. This is due to the self-limitingcharacteristics of the sequential deposition techniques. Further, thistechnique contributes to a near-perfect step coverage over complextopography.

In addition, the thickness of the layer B, shown in FIG. 4, may beeasily controlled while minimizing the resistance of the same byemploying sequential deposition techniques. With reference to FIG. 6 itis seen in the slope of line 50 that the thickness of the tungsten layerB is proportional to the number of cycles employed to form the same. Theresistivity of the tungsten layer, however, is relatively independent ofthe thickness of the layer, as shown by the slope of line 52 in FIG. 7.Thus, employing sequential deposition techniques, the thickness of arefractory metal layer may be easily controlled as a function of thecycling of the process gases introduced into the processing chamber witha negligible effect on the resistivity.

Referring to FIG. 8, control of the deposition rate was found to bedependent upon the temperature of the substrate 42. As shown by theslope of line 54, increasing the temperature of the substrate 42increased the deposition rate of the tungsten layer B. For example, at56, the deposition rate is shown to be approximately 2 Å/cycle at atemperature of 250° C. However at point 56 the deposition rate isapproximately 5 Å/cycle at a temperature of 450° C. The resistivity ofthe tungsten layer, however, is virtually independent of the layerthickness, as shown by the slope of curve 58, shown in FIG. 9. As aresult, the deposition rate of the tungsten layer may be controlled as afunction of temperature without compromising the resistivity of thesame. However, it may be desired to reduce the time necessary to depositan entire layer of a refractory metal.

To that end, a bulk deposition of the refractory metal layer may beincluded in the deposition process. Typically, the bulk deposition ofthe refractory metal occurs after the nucleation layer is formed in acommon processing chamber. Specifically, in the present example,nucleation of a tungsten layer occurs in chamber 12 employing thesequential deposition techniques discussed above, with the substrate 42being heated in the range of 200° C. to 400° C., and the processingchamber 37 being pressurized in the range of 1 Torr to 10 Torr. Anucleation layer 60 of approximately 12 nm to 20 nm is formed on apatterned substrate 42, shown in FIG. 10. As shown, the substrate 42includes a barrier layer 61 and a patterned layer having a plurality ofvias 63. The nucleation layer is formed adjacent to the patterned layercovering the vias 63. As shown, forming the nucleation layer 60employing ALD techniques provides 100% step coverage. To decrease thetime required to form a complete layer of tungsten, a bulk deposition oftungsten onto the nucleation layer 60 occurs using CVD techniques, whilethe substrate 42 is disposed in the same processing chamber 12, shown inFIG. 1. The bulk deposition may be performed using recipes well known inthe art. In this manner, a tungsten layer 65 providing a complete plugfill is achieved on the patterned layer with vias having aspect ratiosof approximately 6:1, shown in FIG. 11.

As mentioned above, in an alternate embodiment of the present invention,the carrier gas may differ from the purge gas, as shown in FIG. 12. Thepurge gas, which is introduced at time intervals t₁, t₃, t₅, and t₇comprises of Ar. The carrier gas, which is introduced at time intervalst₂ and t₆, comprises of N₂. Thus, at time interval t₂ the gasesintroduced into the processing chamber include a mixture of B₂H₆ and N₂,and a time interval t₆, the gas mixture includes B₂H₆ and N₂. The pumpprocess during time intervals t₄ and t₈ is identical to the pump processdiscussed above with respect to FIG. 5.

Referring again to FIG. 2, the process for depositing the tungsten layermay be controlled using a computer program product that is executed bythe controller 22. To that end, the controller 22 includes a centralprocessing unit (CPU) 70, a volatile memory, such as a random accessmemory (RAM) 72 and permanent storage media, such as a floppy disk drivefor use with a floppy diskette, or hard disk drive 74. The computerprogram code can be written in any conventional computer readableprogramming language; for example, 68000 assembly language, C, C++,Pascal, FORTRAN, and the like. Suitable program code is entered into asingle file, or multiple files, using a conventional text editor andstored or embodied in a computer-readable medium, such as the hard diskdrive 74. If the entered code text is in a high level language, the codeis compiled and the resultant compiler code is then linked with anobject code of precompiled WINDOWS® library routines. To execute thelinked and, compiled object code the system user invokes the objectcode, causing the CPU 70 to load the code in RAM 72. The CPU 70 thenreads and executes the code to perform the tasks identified in theprogram.

Although the invention has been described in terms of specificembodiments, one skilled in the art will recognize that various changesto the reaction conditions, i.e., temperature, pressure, film thicknessand the like can be substituted and are meant to be included herein.Additionally, while the deposition process has been described asoccurring in the same chamber, it may be bifurcated. In this manner, thenucleation layer may be deposited in one chamber and the bulk depositionoccurring in a differing chamber, located within the same mainframedeposition system. However, the bulk deposition may occur in aprocessing chamber of a mainframe deposition system that is differentfrom the mainframe deposition system in which the processing chamber islocated that is employed to deposit the nucleation layer. Finally, otherrefractory metals may be deposited, in addition to tungsten, and otherdeposition techniques may be employed in lieu of CVD. For example,physical vapor deposition (PVD) techniques, or a combination of both CVDand PVD techniques may be employed. The scope of the invention shouldnot be based upon the foregoing description. Rather, the scope of theinvention should be determined based upon the claims recited herein,including the full scope of equivalents thereof.

1. A method for forming a tungsten-containing material on a substrate,comprising: forming a tungsten-containing layer by sequentially exposinga substrate to a processing gas and a tungsten-containing gas during anatomic layer deposition process, wherein the processing gas comprises aboron-containing gas and a nitrogen-containing gas; and forming atungsten bulk layer over the tungsten-containing layer by exposing thesubstrate to a deposition gas comprising the tungsten-containing gas anda reactive precursor gas during a chemical vapor deposition process. 2.The method of claim 1, wherein the tungsten-containing gas comprisestungsten hexafluoride.
 3. The method of claim 2, wherein theboron-containing gas comprises diborane.
 4. The method of claim 3,wherein the nitrogen-containing gas comprises dinitrogen.
 5. The methodof claim 3, wherein the substrate is exposed to argon gas prior tosequentially exposing the substrate to the processing gas and thetungsten-containing gas.
 6. The method of claim 1, wherein thetungsten-containing layer is deposited on a silicon-containing layerdisposed on the substrate.
 7. The method of claim 6, wherein thesilicon-containing layer comprises silicon oxide.
 8. The method of claim1, wherein the reactive precursor gas comprises a gas selected from thegroup consisting of silane, hydrogen, argon, and combinations thereof.9. A method for forming a tungsten-containing material on a substrate,comprising: transferring a substrate to a first processing positionwithin a processing system; forming a tungsten-containing layer bysequentially exposing the substrate to a processing gas and atungsten-containing gas at the first processing position during anatomic layer deposition process, wherein the processing gas comprises aboron-containing gas and a nitrogen-containing gas; transferring thesubstrate to a second processing position within the processing system;and forming a tungsten bulk layer over the tungsten-containing layer byexposing the substrate to a deposition gas comprising thetungsten-containing gas and a reactive precursor gas at the secondprocessing position during a chemical vapor deposition process.
 10. Themethod of claim 9, wherein the tungsten-containing gas comprisestungsten hexafluoride.
 11. The method of claim 10, wherein theboron-containing gas comprises diborane.
 12. The method of claim 11,wherein the nitrogen-containing gas comprises dinitrogen.
 13. The methodof claim 11, wherein the substrate is exposed to argon gas prior tosequentially exposing the substrate to the processing gas and thetungsten-containing gas.
 14. The method of claim 9, wherein thetungsten-containing layer is deposited on a silicon-containing layerdisposed on the substrate.
 15. The method of claim 14, wherein thesilicon-containing layer comprises silicon oxide.
 16. The method ofclaim 9, wherein the reactive precursor gas comprises a gas selectedfrom the group consisting of silane, hydrogen, argon, and combinationsthereof.
 17. A method for forming a tungsten-containing material on asubstrate, comprising: forming a tungsten-containing layer by exposing asubstrate to a tungsten-containing gas, diborane, and anitrogen-containing gas during an atomic layer deposition process; andforming a tungsten bulk layer over the tungsten-containing layer byexposing the substrate to a deposition gas comprising thetungsten-containing gas and a reactive precursor gas during a chemicalvapor deposition process.
 18. The method of claim 17, wherein thetungsten-containing gas comprises tungsten hexafluoride.
 19. The methodof claim 18, wherein the nitrogen-containing gas comprises dinitrogen.20. The method of claim 17, wherein the reactive precursor gas comprisesa gas selected from the group consisting of silane, hydrogen, argon, andcombinations thereof.